Mycology

TerminologyMykos: Fungus

Mycoses: A disease caused by a fungus

Mycology: Study of fungi

Characteristics of fungiWidely distributed in nature (air, water, soil, decaying organic debris)~400,000 types (Diverse habitats)Eukaryotic, highly developed cellular structureFacultatively anaerobic/strict aerobicChemotropic, nutrition: by absorptionNonphotosynthetic (distinguishes them from plants and algae)Some are aquatic mainly fresh water, a few marineMost are terrestrial soil or on dead plant material

Characteristics of fungi

Crucial role in mineralisation of organic carbonMany are parasites of terrestrial plantsA few are parasitic on animals including humansGenerally less important than bacterial or viral infectionsUnicellular (yeasts) or filamentous(molds).Rigid cell wall, some are capsulated.Spore bearing stages in the life cycleUsually reproduce by sexual and asexual meansInsensitive to antibacterial antibioticsthey have a diploid number of chromosomes

Characteristics of fungiFungi can be beneficial or harmfulThey are especially harmful to people who are compromised (opportunistic) or are in the hospital for other infections (nosocomial)

Fungi are important in the food chain because they decompose dead plant matter and recycle nutrients

Characteristics of fungiMost fungi prefer a moist environment with a relative humidity of 70% or more. Various species can grow at a temperature ranging from -6 to 50C with optimaltemperature of 20 to 35C.

Most fungi grow well at an acidic pH of 5.0 or lower and thus they grow well on fruits and many vegetables that are acidic in nature.

Structure and functionsA mass of hyphal elements is termed themycelium (synonymous withmold).

Aerial hyphae often produce asexual reproduction propagules termedconidia(synonymous with spores).

Relatively large and complex conidia are termedmacroconidia while the smaller and more simple conidia are termedmicroconidia.When the conidia are enclosed in a sac (the sporangium), they are calledendospores.The presence/absence of conidia and their size, shape and location are major features used in the laboratory to identify the species of fungus in clinical specimens.

Major polysaccharides of fungal cell wallPOLYMERMONOMERChitinN-acetyl glucosamineChitosanD-GlucosamineCelluloseD-Glucose-GlucanD-Glucose-GlucanD-GlucoseMannanD-Mannose

The type and amount of the polysaccharide vary from one fungal species to other.

What are the differences between Fungi and Bacteria?

MetabolismFor medical purposes the important aspects of fungal metabolism are the synthesis of: chitin a polymer of N-acetyl glucosamine, rather than peptidoglycan_ a characterestic component of bacterial cell wall. Fungi are there for unaffected by antibiotics (for example penicillin) that inhibit peptidoglycan synthesis

ergosterol for incorporation into the plasma membrane. This makes the plasma membrane sensitive to those antimicrobial agents which either - block the synthesis of ergosterol or - prevent its incorporation into the membrane or - bind to it, e.g. amphotericin B

The synthesis of toxins such as: a.Ergot alkaloids- these are produced by Claviceps purpureab.Aflatoxins - these are carcinogens produced by Aspergillus flavus when growing on grain. When these grains are eaten by humans or when they are fed to dairy cattle and they get into the milk supply, they affect humans.

The synthesis of proteins on ribosomes that are different from those found in bacteria.

This makes the fungi immune to those antimicrobial agents that are directed against the bacterial ribosome, e.g., chloramphenicol.

Penicillium (Source of penicillin)Morphological structures and types of conidiophore branching in Penicillium. a. simple; b. one-stage branched; c. two-stage branched; d. three-stage branchedIn Penicillium, phialides may be produced singly, in groups or from branched metulae, giving a brush-like appearance known as a penicillus

Penicillin kills bacteria by interfering with their ability to synthesize cell wall.Penicillin quickly became a primary treatment for pneumonia, diphtheria, syphilis, gonorrhea, scarlet fever, and many other infections. For the discovery of penicillin and its curative effect in various infectious diseases Fleming, Chain, and Florey received the Noble Prize for Medicine in 1945.

Fungi as human pathogensAmong the 50 000-250 000 species of fungi that have been described, fewer than 200 have been associated with human disease

Diseases Caused by FungiDiseases caused by fungal cells are called (Mycosis).

Diseases caused by fungal spores are called (Allergy), either respiratory or skin allergy.

Diseases caused by fungal byproducts, mycotoxins, are called (Mycotoxicosis).

Fungi- Morphological Classification Yeast: Unicellular (grows at 37 C)

Mould: Multicellular (grows at 25 C)

Dimorphic: growing in mould or yeast form

Yeast Budding Mother and Daughter Cells

Molds are made of hyphae (cells joined in thread-like strands)

Classification of HyphaeBASED ON:A. Existence of septaSeptate NonseptateB. Shape and Morphology Racquet Spiral Nodular Root-like (rhizoid) Pectinate Chandler

Septa- Regular cross-walls formed in hyphae. Hyphae with septa are septate.Those lacking septa except to delimit reproductive structures and aging hyphae are called aseptate or coenocytic.

Mono and Di Karyotic Monokaryotic: each compartment has a single nucleus

Dikaryotic: two distinct nuclei within each hyphae compartment

Hetero and Homo Karyotic Heterokaryotic: dikaryotic or multinucleate hypha has nuclei from genetically distinct individuals

Homokaryotic: hyphae whose nuclei are genetically similar to one another

DIMORPHICCapable of growing in mould or yeast form under different environmental conditions (temperature, CO2, nutrients)

Some fungal species, specially those that cause systemic mycoses,are dimorphic.

Fungal reproduction Anamorph= asexual stage Mitospore=spore formed via asexual reproduction (mitosis), commonly called a conidium or sporangiospore Teleomorph= sexual stageMeiospore=spore formed via sexual reproduction (e.g., resulting from meiosis), type of spore varies by phylum

Identification of Fungal SpeciesThe presence/absence of conidia and their size, shape and location are major features used in the laboratory to identify the species of fungus in clinical specimens.

Asexual fruiting structure of Rhizopus speciesAsexual fruiting structure of Rhizopus species, illustrating sporangium, sporangiophore, sporangiospores, coenocytic hyphae and rhizoids.

Asexual fruiting structure of Aspergillus speciesAsexual fruiting structure of Aspergillus species, illustrating septate hyphae, conidiophore, vesicle, phialides and conidiospores

Asexual fruiting structure of Penicillium speciesAsexual fruiting structure of Penicillium species, illustrating septate hyphae, conidiophore and conidiospores

Asexual Reproduction by Budding in YeastThe cell grows and divides into two daughter cells that each contain the information and machinery necessary to repeat the process.

Budding Yeast

ASEXUAL SPORES1. Arthrospore2. Blastospore (Budding in Yeast)3. Chlamydospore4. Macroconidium (Relatively large)5. Microconidium (Relatively small)6. Sporangiospore (Sporangia)

Division ChytridiomycotaDivision AscomycotaDivision GlomeromycotaDivision BasidiomycotaDivision ZygomycotaDivision Deuteromycota

Kingdom Fungi

Chytrids (1,000 species)Zygomycetes (1,000 species)Hyphae25 mGlomeromycetes (160 species)Fungal hyphaAscomycetes (65,000 species)Basidiomycetes (30,000 species)Fungus-like protistDeuteromycota?

The five fungal phyla can be distinguished by their reproductive features.

mainly aquatic.Some are saprobes, while others parasitize protists, plants, and animals. chitinous cell wallflagellated zoospores the most primitive fungiDivision Chytridiomycota

Division AscomycotaSac fungi (truffles, yeast)Beer > 6,000 yearsWine > 8,000 yearsLichensDecomposers, pathogens60,000 speciesyeast describes a form of fungi (i.e., non-hyphal)

Division AscomycotaScarlet cuptrufflesMorchella

Roquefort cheeseClose up of cheese showing blue-green mycelium of Penicillium roqueforti.Division Ascomycota

LICHENSYeastLichen

Division GlomeromycotaPreviously With ZygomycotaSmall Monophyletic CladeEndomycorrhizae Arbuscular MycorrhizaeProduce branching Arbuscules

Plant-Fungal RelationshipsMycorrhizae (fungus roots)90% of tree species have this associationVery important to absorption of water and nutrients

Soil surfacePlant rootsMycorrhizaeIncreases s.a. for absorption

Division BasidiomycotaClub fungi (mushrooms)Club-shaped reproductive structureFoodPlant diseases25,000 species

Fairy Ring

Division Zygomycotae.g. Rhizopus sp. (Black bread Mold)

ZygomycosisCaused by:Rhizopus sp.Absidia sp.Mucor sp.

Candidiasiscaused by Candida albicansCandidiasis or yeast infectionCan be thrush (oral) or vulvovaginal candidiasisFound in newborns, AIDS patients, and in people who have just completed antibioticIs also one cause of diaper rash!

Yeast Infections

Division DeuteromycotaPenicilliumOrganisms from this phylum are both beneficial (penicillin from Penicillium, soy sauce and citric acid from Aspergillus) and very harmful (Aspergillus can be toxic if inhaled).Spores produced by the species in this category are not quite so easy to categorize by shape.

Aspergillus sp.

Aspergillosis Aspergillus causes aspergillosis

Penicillium sp.

Clinical Mucology

Classification of Fungal Infections In general, humans have a high level of innate immunity to fungi and most of the infections they cause are mild and self-limiting.This resistance is due to:Fatty acid content of the skin mucosal surfaces body fluidsEpithelial turnover

Normal floraTransferrin Transferrin is a blood plasma protein binds iron, thus creating an environment low in free iron, where few microbes are able to survive associated with the innate immune system Cilia of respiratory tract

Fungal diseasesAny fungal infection is a mycosisThese are long lasting and hard to treatClassify these into 4 groups according to degree of tissue involvement and mode of entry into host:

1- Systemic (endemic)2- subcutaneous 3- Cutaneous4- opportunistic

Systemic Infections deep in the bodyCan affect a number of tissues and/or organsUsually caused by inhalation of spores from fungi that live in the soilInfections that originate primarily in the lung and may spread to many organ systems. Include histoplasmosis and coccidioidomycosis

Systemic mycoses(1) Histoplasma capsulatum (causing histoplasmosis) Dimorphic with mold to yeast transition when infecting susceptible species. Yeast cells are relatively small. Saprobic phase shows tuberculate macroconidia

Saprobic Phase Parasitic Phase

Systemic mycoses(2) Blastomyces dermatitidis (causing blastomycosis) Dimorphic with mold to yeast transition when infecting susceptible species. Yeast cells are medium size with thick walls. Saprobic Phase Parasitic Phase

Systemic mycoses (3) Paracoccidioides brasiliensis (causing paracoccidiodomycosis) Dimorphic with mold to yeast transition when infecting susceptible species. Yeast cells have multiple buds

Saprobic Phase Parasitic Phase

Systemic mycoses (4) Coccidioides immitis (causing coccidioidomycosis) Dimorphic with mold tospherule transition when infecting susceptible species. Spherules are multinucleate. Saprobic Phase Parasitic Phase

Systemic mycoses (5) Cryptococcus neoformans (causing a severe form of meningitis in people with HIV infection and AIDS). Monomorphic with yeast phase only. Saprobic Phase Parasitic Phase This is the only pathogenic yeast with a capsule. The capsule is extremely large.

subcutaneousInfections beneath the skinInfections involving the dermis, subcutaneous tissues, muscle or boneIt Caused by saprophytic fungi that live in soil or on vegetationOften enter through puncture woundExample is sporotrichosis

Subcutaneous mycoses

DiseaseEtiological AgentSymptomsIdentification of OrganismSporotrichosisSporothrix schenckiiNodules and ulcers along lymphatics at site of inoculationBudding yeast in tissue exudate that converts to mold with "rosette pattern" of conidiation on culture at 25oC.ChromoblastomycosisFonsecaea pedrosoi Fonsecaea compacta Wangiella dermatitidisWarty nodules that progress to "cauliflower-like" appearance at site of inoculationCopper-colored spherical yeast called "Medlar bodies" in tissueMycetomaPseudallescheria boydii Madurella grisea Madurella mycetomatisDraining sinus tracts at site of inoculationWhite, brown, yellow or black granules in exudate that are fungal colonies

Cutaneous Fungi that infect only hair, epidermis, and nails are dermatophytes or cutaneous mycosesThese produce an enzyme that degrades keratin (keratinase)Can spread by contact (human/human, animal/human)All of the dermatophytic diseases are caused by members of three genera, Microsporum, Trichophyton and Epidermophyton, which comprise 41 species.

- There is some specificity, however. Whereas all three organisms attack the skin, Microsporum does not infect nails, and Epidermophyton does not infect hair. - They do not invade underlying, non keratinized tissues. Tinea capitis of the scalp caused by Microsporum gypseum

Cutaneous mycoses

DiseaseEtiological AgentSymptomsIndentification of organismTinea capitisMicrosporum sp. Trichophyton sp. Epidermophyton sp.ringworm lesion of scalppresence/absence and shape of micro- and macroconidia in scrapings from lesionTinea corporisMicrosporum sp. Trichophyton sp. Epidermophyton springworm lesion of trunk, arms, legspresence/absence and shape of micro- and macroconidia in scrapings from lesionTinea manusMicrosporum sp. Trichophyton sp. Epidermophyton springworm lesion of handpresence/absence and shape of micro- and macroconidia in scrapings from lesionTinea cruris "jock itch"Microsporum sp. Trichophyton sp. Epidermophyton springworm lesion of groinpresence/absence and shape of micro- and macroconidia in scrapings from lesionTinea pedis"athlete's foot"Microsporum sp. Trichophyton sp. Epidermophyton springworm lesion of footpresence/absence and shape of micro- and macroconidia in scrapings from lesionTinea unguiumMicrosporum sp. Trichophyton sp. Epidermophyton spinfection of nailspresence/absence and shape of micro- and macroconidia in scrapings from lesionEctothrixMicrosporum sp. Trichophyton sp. Epidermophyton spinfection of hair shaft surfacemycelium and spores on hair shaftEndothrixMicrosporum sp. Trichophyton sp. Epidermophyton spinfection of hair shaft interiormycelium and spores in hair shaft

Opportunistic mycosesHarmless in normal habitat but can become pathogenic if given the opportunityInfections in patients with immune deficiencies who would otherwise not be infected Opportunistic mycoses are seen in those people with impaired host defenses such as occurs in: AIDS Alteration of normal flora Diabetes mellitus Immunosuppressive therapy Malignancy

Opportunistic mycoses

DiseaseEtiological AgentSymptomsIdentification of organismCandidiasesCandida albicansCreamy growth on various areas of bodyBudding yeast, septate hyphae, pseudohyphae in tissue. Germ tubeformation in serumAspergillosisAspergillus fumigatus"Fungus ball" in tissueMorphology of asexual fruiting structureZygomycosisRhizopus sp. Absidia sp. Mucor sp.VariousMorphology of asexual fruiting structure and mycelium

LABORATORY DIAGNOSIS OF MYCOSESDirect microscopic examinationGram, potassium hydroxide (KOH), calcofluor white, India inkCulture Sabouraud dextrose agar Mycobiotic agarSerology

LABORATORY DIAGNOSIS OF MYCOSESVisualization of fungi in human tissue preparations1. Treatment with 10% potassium hydroxide 2. Positive stain with: a.Lactophenol cotton blue b.Grocott silver stain c.Hematoxylin d.Eosin 3. Negative stain with India ink Fluorescence of fungi under ultraviolet light

Stained Fungi Hematoxylin-eosin-stained section of cerebral cortex demonstrating septate hyphal elements.India Ink of Cerebro-Spinal Fluid (CSF)with Cryptococcus neoformans Gram Stain of tissue infected with Cryptococcus neoformans

Clinical Techniques in MycologyCulture of fungi on 1.Sabouraud's agar (favors fungal growth because of low pH)2.Mycosel agar (selective for pathogenic fungi because of chloramphenicol and cycloheximide in medium)

Visualization of cultured fungi (25oC and 37oC) 1. Colony morphology2. Cellular morphology a. Hyphal morphology (1) Aseptate or coenocytic (2) Septate (a) Regular connection (b) Clamp connection

***************Figure: 02-01a-b

Caption:Internal structure of microbial cells. (a) Diagram of a prokaryote. (b) Diagram of a eukaryote.

******* In this sequence, Escherichia coli were incubated in penicillin for 30 minutes. The bacteria lengthen, but cannot divide. Eventually the weak cell wall ruptures (last panel). ******MODULAR GROWTH - FRAGMENTATION = ASEXUAL REPRODUCTION!! *******************************************************